1. Department of Obstetrics and Gynecology, Sanggyepaik Hospital, Inje University College of Medicine, Asan Medical Center, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Asan Medical Center, Seoul, Korea.
3. Department of Obstetrics and Gynecology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.